Pilot study findings from humans in our laboratory demonstrate our ability to fully characterize the "open-loop" carotid baroreflexes to operate at a higher carotid sinus distending pressure (classic resetting). in both dogs and humans the role of the aortic- baroreceptors in regulating blood pressure during exercise is unknown. We have documented in humans discrete differential roles of the aortic and carotid baroreceptor reflexes in regulating blood pressure at rest as well as identifying an interaction between cardiopulmonary baroreceptors and carotid baroreflexes. In addition, these reflexes and their interactions operate differently in individuals of differing levels of maximal aerobic capacity aerobic capacity (VO-2max) and may operate differently in men compared to women. Therefore, we hypothesize that information received from the carotid, aortic and cardiopulmonary baroreceptors are the principal modulators of systemic blood pressure during dynamic exercise in the human, and that this relationship is altered by the individual's level of aerobic fitness. In order to test the fallibility of these hypotheses, we will define the stimulus-response relationships and the interactions of the aortic. carotid and cardiopulmonary reflexes during steady-state exercise in individuals with high and low maximal aerobic capacities. Many of the experimental procedures and their modifications for use during exercise have been developed in our laboratory. Specifically, we will use different intensity steady-state work to establish a regulated blood pressure, neck pressure/suction techniques for perturbing the carotid sinus, lower body negative pressure and acute volume expansion to alter central venous pressure, and pharmacologic and mechanical means of non-invasively isolating the aortic baroreceptor reflex. The proposed studies will investigate the physiological mechanisms and will determine gender differences. The findings will provide important baseline information concerning the interactions of the various baroreceptor populations on the regulation of blood pressure during exercise.